[MiKTeX] Problems with Fonts

[Luis <lu...@ua...>]

    Dear all

    I make slides with package prosper.

    In some equations some parentises do not appear.

    $v_i= \left( s+1\right)/2$

     The \left( ou \right) have no effect.

     That happens in two computers with Miktex instalation.

     It start to happen when I update Miktex.

     Thanks

     Luis Gonçalves